This study investigates the potential of recycled concrete (rBet) as a sustainable filler for both neat polypropylene (PP) and recycled polypropylene (rPP), contributing to the transition toward a circular economy through increased utilization of waste-derived materials. RBet obtained from laboratory concrete waste was processed by grinding and sieving into a fine powder with an average particle size of 12.5 μm. Composites containing 15, 30, and 45 wt% rBet were produced with and without maleic anhydride grafted polypropylene (MAPP) as a coupling agent (1-3 wt%). The materials were compounded using a twin-screw extruder and injection molded into test specimens.

Thermal behavior was characterized by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA), while mechanical performance was assessed through tensile and impact testing. The results showed that addition of rBet significantly increased stiffness (Young's modulus) but reduced tensile strength and elongation at break, indicating a transition toward brittle behavior at higher loadings. Impact toughness remained relatively stable across rBet contents, with most values generally ranging around 120-130 kJ/m² and showing no systematic decrease. DSC analysis revealed that PP exhibited higher crystallinity than recycled polypropylene, while rBet had a limited influence when normalized to polymer content. The inorganic rBet fraction increased thermal stability, evidenced by higher residual mass in TGA.

Overall, the findings demonstrate that rBet can serve as an effective filler in both neat and recycled polypropylene, with tunable properties depending on filler content and coupling agent concentration. The combined thermal and mechanical analyses provide valuable insight into structure-property relationships governing these sustainable composite systems.